The invention relates to an interface device for tensioning or relaxing a bolt in a nut-and-bolt assembly.
Hydraulic bolt tensioning exits already for many years. In the prior art a hydraulic bolt tensioning tool has been reported which provides a quick and easy method for tightening large diameter bolts to high and accurate pre-loads. Unlike earlier methods it does not use torque and does not require any forceful turning of the nut or bolt, like impact wrenches, flogging spanners or hydraulic torque wrenches. All of the older methods have one common problem, namely friction. Overcoming thread friction and friction between the nut and the washer uses up over 80% of the torque energy applied to the nut or bolt, leaving less than 20% of the energy to produce useful tension in the shank of the bolt. Variations in this friction loss, from bolt to bolt causes non-uniform tension in bolts that have been tightened to the same torque or impact wrench setting.
The known hydraulic bolt tensioner, such as the Boltight™ hydraulic bolt tensioner, is an annular jack, which fits over the bolt and nut to be tightened. The jack pushes against the bolted joint and pulls on the end of the bolt, which needs to be at least one diameter longer to accommodate the bolt-tensioning tool. Because the force produced, by the jack, is applied directly to the end of the bolt, a tension equal to the load generated by the jack is developed in the shank of the bolt. With the jack applying the tension, it is possible to turn the nut with zero torque until it is tight. The load applied by the jack is then relaxed and a high percentage, depending on the length of the bolt and its diameter, is retained in the shank of the bolt. Bolt tensioning tools can be ganged together to enable multiple bolts to be tightened simultaneously, to the same high and accurate pre-load. This is particularly useful when compressing gaskets in pipeline or pressure vessel flanged connections. The high load developed by the multiple bolt tensioning tools, is evenly distributed around the join causing the gasket to flow into the surface irregularities of the flange giving a much better seal.
Flexible hoses with self-sealing quick connect couplings are used to gang the bolt tensioning tools together to form a hydraulic ring main. The ring main and tensioning tools are normally pressurised using an air driven pump working from a compressed air supply.
A severe disadvantage of the known hydraulic tensioner is that the required diameter of the hydraulic cylinder in the jack is directly proportional to the required tension in the shank of the bolt at a given pressure of the hydraulic cylinder. So, at a given pressure in the cylinder, a larger required tension means a larger diameter of the jack in order to produce the required force.
In certain applications, like the pipeline or pressure vessel flanged connections, such space may not always be available.